Slow rotational speed alarm

ABSTRACT

A digital alarm that produces a signal when a function that is being monitored falls below a preset alarm point. The monitored function may be the speed of a shaft. Input pulses representing the function to be monitored are fed into the device and the period of the input pulses are compared with the interval of a signal generated by a monostable multivibrator within the device. If the input signal period is greater than the multivibrator interval, the alarm sounds, but if the input signal period is less than the multivibrator interval the alarm is off. When the alarm is driven either off or on, it is held there until the monitored function changes to the complement condition.

United States Patent 1191 Fathauer SLOW ROTATIONAL SPEED ALARM [75]Inventor: George H. Fathauer, Decatur, Ill.

[73] Assignee: Dickey-john Corporation, Chatham,

Ill.

22 Filed: Aug. 19,1971

21 Appl. No.: 173,138

52 us. c|..... ...'.....340/271, 340/248 P, 3401263,

. 340/267R 51 1111.0. G081 21/00 [58] Field ofSearch IMO/271,263, 248 P,

[56] References Cited UNITEDYSTATES PATENTS 3,611,343 10/1971 Schoenbach340/271 3,370,236 2/1968 Buss ..340/263 3,583,405 6/1971 Gerhardt......340/271 2,984,789 5/1961 OBrien ..340/248P 2,996,630 8/1961Bensemaetalm. ..340/248PX 1451 June 12,1973

3,146,432 8/1964 Johnson 340/271 X 3,500,375 3/1970 Klimo 340/271 XPrimary Examiner-David L. Trafton Attorney-Roy H. Olson, Richard R.Trexler and Richard Bushnell et a].

57 I ABSTRACT A digital alarm that produces a signal when a functionthat is being monitored falls below a preset alarm point. The monitoredfunction may be the speed of a shaft. Input pulses representing thefunction to be monitored are fed into the device and the period of theinput pulses are compared with the interval of a signal generated by amonostable multivibrator within the device. If the input signal periodis greater than the multivibrator interval, the alarm sounds,but if theinput signal period is less than the multivibrator interval the alarm isoff. When the alarm is driven either off or on, it is held there untilthe monitored function changes to the complement condition.

10 Claims, 4 Drawing; Figures Patented June 12, 1973 SLOW ROTATIONALSPEED ALARM BACKGROUND OF THE INVENTION This invention relates to alarmsfor indicating that a function, such as the speed of a rotating shaft,is less than a preselected amount. In many types of machines, apparatusand systems, it is necessary or desirable to monitor a condition orfunction and to provide for an alarm that produces a signal when thecondition or function departs from a preselected value. For example, insome machines it is desirable to monitor the speed of rotation of ashaft and to sound an alarm when the speed of the shaft drops below apreselected amount. In agricultural equipmentsuch as combines,

planters, and the like, the monitoring and alarmsignalling of a slowdownof the speed of a shaft is important so that potential trouble can bedetected early and the situation remedied before more seriousdifficulties or possible breakdown occurs. This is of particularimportance in 'a combine which has a numberof functions orsub-assemblies each of which may have a critical shaft that shouldbemonitored so that a slowdown condition may bepromptly detected.

OBJECTS AND SUMMARY OF THE INVENTION- It is an object of the presentinvention to provide an alarm for indicating that the magnitude of afunction has dropped below a predetermined level. The alarm embodiescircuitry that is particularly suitable for monitoring the speed ofrotation of a shaft, although the alarm may be used to monitor otherfunctions (e.g. pressure, voltage, temperature etc.) which may beconverted to digital form for compatibility with the circuit of theinvention.

A further object of this invention is to provide a digital alarm whichhas a rapid response and is, therefore, capable of rapid detection andalarm-signalling when the function to be monitored has an output belowthe predetermined or preset output.

In accordance with one form of the invention, a machine, such as acombine, has a shaft, the speed of which is to be monitored. A sensingdevice generates input pulses at a frequency proportional to the speedof the shaft. The circuitry of the alarm generates a reference signal ofpredetermined duration relative to a preselected speed for the shaft.The circuitry provides for an arrangement that compares the interval ofthe input shafts of the combine. In such case, each shaft has its ownsensor, and the console may embody separate speed-set controls for eachshaft. Each speed set control and sensor may be selectively switchedinto the alarm circuitry, as desired, depending upon which shaft theoperator desires to monitor.

BRIEF DESCRIPTION OF THE FIGURES In the drawing: 7 FIG. 1 is a sideelevational view, matic in form, of a combine that utilizes an alarmconstructed in accordance with the present invention;

FIG. 2 is a circuit diagram of the alarm; and

FIGS. 3 and 4 are wave forms showing the signals in the fast and slowconditions at certain points in the circuitry of FIG. 2. 7

Referring now in more detail to the drawing, FIG. 1 shows a combine 20having the usual known functions or sub-assemblies that perform thevarious operations of the combine. These are known and will not bedescribed in detail. Suffice it to say, however, for the presentinvention the combine has a conventional cylinder 22 with a cylindershaft 24. By way of example, the present invention will be describedwith reference to monitoring the speed of the cylinder shaft 24although, as heretofore pointed out, the invention may be applied tomonitoring the speed of any other shaft of the combine, or the shafts ofother machines, or to monitor various analog functions of other devicesor systems.

Referring now to FIG. 2, the shaft 24 is shown diagrammatically toinclude a magnet 26 for actuating a reed switch 28 that constitutes apulse generator operated by the shaft 24. The reed switch 28 isconnected across power supply terminals 30, 32 through resistance R1 sothat upon closure of the reed switch 28, an input pulse will appear onconductors 34, 36. The ter minals 30, 32 may be tapped from the batteryof the combine. One magnet 26 is illustrated, which would mean that thereed switch 28 would close once during each revolution of the shaft 24.However, more than one magnet 26 may be used and with the magnets beingequally spaced arcuately about the circumference, of the shaft 24. Inany event, the magnet or mag'nets'26 in cooperation with theree d switch28 provides for a generation of input pulses proportional to the speedof rotation of the shaft 24. Obviously, other forms of pulse generatorsmay be usedrThe conductors 34, 36 may be cabled together and extend fromthe reed switch to the cab of the combine where the remaining circuitry,to be hereinafter described, may be housed in a console or in any othersuitable manner.

The circuit shown in FIG. 2 comprises .resistors Rl through R11inclusive, capacitors Cl through C4 inclulamp and with the lamp beingnormally on in the fast I "sive, transistorsQl through Q3 inclusive,diode D1, set speed potentiometer P, and the integrated circuit (type380) having terminals numbered 1 through .14 inclusive. These terminalscorrespond to the standard numbering-of the terminals for thisintegrated circuit. Furthermore, as will be seen'from the logicdjagramwithin the integrated circuit, the 'lattenis a quad 2-input NOR gatecircuit made up of the four NOR gates a, b, c, d. The values of theresistors are shown in ohms or thousands of ohms, as'the case may be,and the values of the capacitors are indicated in microfarads. The typesof transistors for-Q1 and 02 are shown; the type of tran sistor for Q3will depend upon the nature of the alarm' 38. The lowspeedlamp'l. may bea type 1892 lamp.

somewhat diagram- With the parameters indicated, resistor R4 provides aload resistance for the collector of transistor Q1 while resistor R7 isa dropping resistor so that the power supply terminal 8 of theintegrated circuit is at the proper voltage. Resistor R8 serves as acurrent limiter to the base of transistor Q3 when the latter is turnedon, and capacitor C4 is a power-supply filter capacitor. The resistancenetworks R10, R11 provide a divided down d.c. voltage to the set speedpotentiometer P to make the setting of the latter independent offluctuations of power supply voltage. The purpose of the potentiometer Pwill be hereinafter more fully described. Resistor R6 serves as an inputresistor to the base of transistor Q2 while R is used to provide animpedance so that diode D1 can function.

The NOR gate a and the transistor Q1 cooperate to provide a monostablemultivibrator that is triggered by an input signal through capacitor C1when the reed switch 28 closes. The time interval of the multivibratoris determined by the setting of the set speed potentiometer P and isused as a reference signal. For this purpose the potentiometer P may besuitably calibrated in rpm if the function being monitored is a rotatingshaft. Transistor O1 is normally on as a result of the bias on its basefrom the set speed potentiometer P. The collector of O1 is at a state 0when O1 is on, and this zero input appears at terminal 10, which is oneinput of the NOR gate a. Before a signal is received from the inputthrough capacitor C1 to terminal 9, the other input (terminal of NORgate a, is also at state 0. Consequently, the output of the NOR gate aat terminal 14 is at state I. When a pulse arrives through capacitor C1to terminal 9 causing the signal at terminal 9 to go to state I, theoutput of NOR gate a at terminal 14 goes to state 0. Consequently, thevoltage at the base of collector Q1 drops shutting off 01. The collectorof Q1 now rises to state 1, and this signal is applied over conductors40, 42 to input terminal 10 of NOR gate a. Consequently, the output ofNOR gate a at terminal 14 and conductor 44 is held at a state 0. Thevoltage across the base of transistor 01 rises as determined by the timeconstant of potentiometer P and capacitor C3 to hold the multivibratoron for its preset time. The wave forms on the collector of Q1 and henceon conductors 40, 42 is shown at 46in FIGS. 3 and 4.

The signal on the collector of transistor 01 is also sent over conductor47 and through capacitor C2 to conductor 48 and terminal 5, which is aninput to NOR gate d. The wave form of the signal on conductor 48 isshown at 50 in FIGS. 3 and 4 and is the Q1 collector signaldifferentiated in accordance with the values of capacitor.C2 andresistor R3. The signal input through capacitor C1 is also sent overconductor 52 to terminal 6 which is an input terminal of- NOR gate 0.The wave form of this input signal to terminal 6 is shown at 54 in FIGS.3 and'4 and is a differentiated input signal a's'determined by thevalues of capacitor C1 and resistor R2. For reasons hereinafter morefully explained, the signal shown at 50 is differentiated with a longertime constant than is the signal shown at 54 with the result that thesignal or pulse 50 is of longer duration than that of the pulse orsignal 54. The NOR gates c, d form a flipflop which is a set-resetmemory circuit wherein an input pulse at terminal 5 constitutes a setpulse while an input pulse at terminal 6 constitutes a reset pulse.Because the set and reset pulses are differentiated'with different timeconstants, as aforesaid, the set pulse will override the reset pulsewhen the two are applied together at the beginning of a multivibratorinterval. The output of this flip-flop is from NOR gate d to terminal 3,and this, output is connected through conductor 56 to the input terminal12 of NOR gate b.

The output of NOR gate b at terminal 13 is sent over conductor 58 to thebase of transistor Q2 which will conduct to turn on the lamp L when thesignal at terminal l3 and on conductor 58 is at state I. A feedback fromthe collector of transis-tor Q2 on conductor 60 to input terminal 11 ofNOR gate b serves, in cooperation with NOR gate b, to latch Q2 off oron, as the case may be.

Since transistor 02 drives transistor Q3 the alarm 38 (buzzer, bell,etc.) is turned on at the same time the lamp L is turned on. Likewise,when 02 is turned off, the lamp L and alarm 38 will be turned off. Insome embodiments of the invention it is not necessary to have both thelamp L and alarm 38. In fact, the invention encompasses the use of anysignalling or indicating device that is actuated under control oftransistor Q2 or other switching device.

If the shaft 24 is rotating in a fast condition, the input pulses 60(FIG. 3) on conductors 34, 36 are sent out faster than the preselectedmultivibrator interval as represented by the width of the pulse 46 onthe collector of transistor Q1..If the lamp L and alarm 38 hadpreviously been on, then transistor Q2 would be on. This is due to thefact that the inputs at terminals 11, 12 to NOR gate b would both be atstate 0 causing the output of that gate at terminal 13 and conductor 58to be at state 1. The reset pulse 54a (FIG. 3) that follows the turn-onof the multivibrator is applied from conductor 52 to terminal 6. Thiscauses terminal 3 to go to state I (see wave form 62, FIG. 3) and put astate I on conductor 56 and at input terminal 12. When an input state Iisthus supplied to terminal 12, the output at terminal 13 (see wave fonn64, FIG. 3) and on conductor 58 will go to state 0 and shut offtransistor 02, thereby turning off the lamp L and alarm 38. When 02turns off, the signal on conductor 60 goes from state 0 to state 1 toprovide a holding signal to latch Q2 off because the signal on terminal13 and conductor 58 cannot go to state 1 so long as there is a state Ion conductor 60.

Q2 will not turn on to trigger the signalling devices so long assubsequent input pulses on conductors 34, 36 have an interval which isless than theinterval of the multivibrator. This condition resultsbecause of the reset pulse 54a on terminal 6, which occurs before theend of the multivibrator interval. The reset pulse 54a changes the stateof terminal 12 to a state I. At this time terminals 1 1 and 12 are bothat state I so terminal 13 stays at state 0. At the end of themultivibrator interval, 01 again conducts dropping its collector andconductor 42 to a state 0. Diode D1 is shown connected from terminal 11to the Q1 collector via conductor 42. The voltage drop on conductor 42due to the 01 turnon causes diode D1 to conduct, thereby dropping thevoltage at terminal 11 to a state 0. However, terminal 13 still remainsat state 0 due to reset pulse 54a that was applied before the end of themultivibrator interval.

If the shaft 24 now slows down below the desired speed in accordancewith the setting of potentiometer P, the conditions of the various waveforms will appear as shown in FIG. 4. There it should be noted that thesignal toterminalS was differentiated with a substantially longer timeconstant than was the signal 54. Consequently, the same is true withrespect to the signals 50b, 54b. As a result, the set pulse 50b onconductor 48 and terminal 5 overrides or cancels out the effect of thereset pulse 54b on conductor 52 and terminal 6. This keeps the flipflopin a set condition whereby the output on conductor 56 is maintained at astate 0. This output is, of course, delivered as state to input terminal12 of NOR gate b. However, the output of NOR gate b will not changestate unless the input at terminal 11 is also changed to state 0. Thischange of state at terminal 11 is effected by the turning on of Q1. atthe end of the multivibrator interval, it being remembered that in theslow condition no reset pulse will be applied to terminal 6 before theend of the multivibrator interval. With Q1 now on, the voltage on Q1collector and on conductor 42 will drop and cause a conduction throughdiode D1 to drop the signal level at terminal 11 to a state 0. Now, bothterminals 11 and 12 are at state 0 causing NOR gate b to have an outputon conductor 58 at state 1 to turn on transistor Q2. Subsequent setsignals applied to input terminal continue to cancel out the resetsignals. Thus, with state 0 on conductor 60 and terminal 11 and also onterminal 12, transistor Q2 is maintained on to actuate continuously thesignalling devices L and 38 until a fast condition is restored. Thesignals 62;, 64s for terminals 3 and 13 are seen to be at states 0 and 1respectively in FIG. 4 after turn-on of Q2.

While the potentiometer P may be used to adjust the time interval of themultivibrator to correspond with the alarm point, it may be desired tohave a deadband or percentage speed change between the turnon point(fast to slow) and tum-off point (slow to fast). Thus, when the shaft isspeeding up from a slow condition the lamp and alarm will turn off whenone speed is reached. However, when the shaft is going from a fast to aslow condition, the lamp and alarm will turn on at another and lowerspeed. The use of the dead-band avoids the necessity of criticalset-speed settings of the potentiometer P. It also insures that when theequipment begins operating that shaft has initially gone to a speed thatis safely above the minimum desired speed.

' Provision of the dead-band may be made by the use of resistor R9 whichsupplies a portion of the signalfrom conductor 60 to the multivibratorto lengthen the multivibrator time interval when the lamp is offrelative to the time interval when the lamp is on. The effect of R9 inthe circuit is, therefore, to start the voltage drop on capacitor C3 ata higher voltage than if R9 were not present so that it takes a greatertime for Q1 to turn on after being turned off whereby the multivibratorinterval is increased for the lamp-off condition.

The invention is claimed as follows:

1. In a machine having a shaft, an alarm for indicating that said shaftis moving at less than at a preselected speed, said alarm comprisingmeans for generating input pulses at a frequency proportional to thespeed of the shaft, means for generating a reference signal ofpredetermined duration relative to said preselected speed, signallingmeans having a normal and a signalling condition, means comparing thereference signal duration with the input signal interval for actuatingsaid signalling means to give a signalling condition only when the inputpulse interval is greater than the duration of said reference signal,said last-named means comprising a set-reset memory circuit thatproduces an output signal at one binary logic state when set and anoutput signal at the complement binary logic state when reset, a gatingcircuit having an output determined by an input and the output signal ofsaid memory circuit, the output state of said gating circuit determiningthe condition of said. signalling means,and means for providing a setinput to said memory circuit at the end of said predetermined durationof the reference signal.

2. In a machine according to claim 1, said means for generating areference signal comprising a monostable multivibrator that is triggeredby an input pulse.

3. In a machine according to claim 1, said means for actuating saidsignalling means further comprising setreset latch circuitry forlatching said signalling means in the condition to which the signallingmeans is driven, said latch circuitry including said gating circuit.

4. In a machine according to claim 1, said machine being a combine andsaid shaft being a power driven shaft thereon.

5. An alarm for indicating that the output of a func tion is less thanat a preselected amount, said alarm comprising means for generatinginput pulses at a frequency proportional to theanalog function, amonostable multivibrator for generating a reference signal ofpredetermined duration relative to said preselected magnitude of saidanalog function, said multivibrator being triggered by an input pulse,signalling means, and means for actuating said signalling means toproduce a signalling condition when the input pulse interval is greaterthan the duration of said reference signal; said last-named meanscomprising a set-reset memory circuit having an output at one binarylogic state when set and an output at the complement binary logic statewhen reset, means responsive to the input pulse following the pulse thattriggers the multivibrator for providing a reset pulse for said memorycircuit, and means comprising an input to said memory circuit from theoutput of said multivibrator for providing a set pulse for said memorycircuit at the end of the multivibrator interval that cancels the effectof said reset pulse when the input pulse frequency is less than theduration of said reference signal.

6. An alarm according to claim 5 in which the set pulse is derived by adifferentiation of the reference sig nal and the reset pulse is derivedby a differentiation of the input pulses, the reset pulse having ashorter time constant than that of the set pulse.

7. An alarm according to claim 5 including adjusting means for varyingthe duration of said reference signal.

8. An alarm according to claim 5 including a set-reset latch circuitforming part of said actuating means for latching said signalling meansin a signalling condition or in non-signalling condition when driventhereto; said latch circuit including a transistor that constitutes aswitch for said signalling means, and a logic gate, the transistorhaving a collector connected to an input of the logic gate and the logicgate having an output connected to the base of the transistor.

9. An alarm according to claim including means for increasing theduration of the reference signal when the signalling device is oncompared to the duration of said reference signal when the signallingdevice is off.

10. Circuitry having signalling means and means for actuating thesignalling means, said actuating means including a flip-flop having setand reset inputs and an output, said output being at one binary logicstate when triggered by a pulse at the set input and being at thecomplement state when triggered by a pulse at the reset input, means forgenerating i'nput pulses to said reset input, and circuit meansincluding a monostable multivibrator triggered by a signal at the resetinput, said mined duration, said circuit means applying set pulses tosaid set input through the output of said multivibrator, the resetpulses preventing setting of said flip-flop if received from saidgenerating means at intervals greater than the duration of saidmultivibrator signal, said set pulse being of such magnitude andduration as to cancel the effect of a reset pulse if an input pulse isreceived at said reset input after the duration of said multivibratorsignal.

1. In a machine having a shaft, an alarm for indicating that said shaftis moving at less than at a preselected speed, said alarm comprisingmeans for generating input pulses at a frequency proportional to thespeed of the shaft, means for generating a reference signal ofpredetermined duration relative to said preselected speed, signallingmeans having a normal and a signalling condition, means comparing thereference signal duration with the input signal interval for actuatingsaid signalling means to give a signalling condition only when the inputpulse interval is greater than the duration of said reference signal,said last-named means comprising a set-reset memory circuit thatproduces an output signal at one binary logic state when set and anoutput signal at the complement binary logic state when reset, a gatingcircuit having an output determineD by an input and the output signal ofsaid memory circuit, the output state of said gating circuit determiningthe condition of said signalling means,and means for providing a setinput to said memory circuit at the end of said predetermined durationof the reference signal.
 2. In a machine according to claim 1, saidmeans for generating a reference signal comprising a monostablemultivibrator that is triggered by an input pulse.
 3. In a machineaccording to claim 1, said means for actuating said signalling meansfurther comprising set-reset latch circuitry for latching saidsignalling means in the condition to which the signalling means isdriven, said latch circuitry including said gating circuit.
 4. In amachine according to claim 1, said machine being a combine and saidshaft being a power driven shaft thereon.
 5. An alarm for indicatingthat the output of a function is less than at a preselected amount, saidalarm comprising means for generating input pulses at a frequencyproportional to the analog function, a monostable multivibrator forgenerating a reference signal of predetermined duration relative to saidpreselected magnitude of said analog function, said multivibrator beingtriggered by an input pulse, signalling means, and means for actuatingsaid signalling means to produce a signalling condition when the inputpulse interval is greater than the duration of said reference signal;said last-named means comprising a set-reset memory circuit having anoutput at one binary logic state when set and an output at thecomplement binary logic state when reset, means responsive to the inputpulse following the pulse that triggers the multivibrator for providinga reset pulse for said memory circuit, and means comprising an input tosaid memory circuit from the output of said multivibrator for providinga set pulse for said memory circuit at the end of the multivibratorinterval that cancels the effect of said reset pulse when the inputpulse frequency is less than the duration of said reference signal. 6.An alarm according to claim 5 in which the set pulse is derived by adifferentiation of the reference signal and the reset pulse is derivedby a differentiation of the input pulses, the reset pulse having ashorter time constant than that of the set pulse.
 7. An alarm accordingto claim 5 including adjusting means for varying the duration of saidreference signal.
 8. An alarm according to claim 5 including a set-resetlatch circuit forming part of said actuating means for latching saidsignalling means in a signalling condition or in non-signallingcondition when driven thereto; said latch circuit including a transistorthat constitutes a switch for said signalling means, and a logic gate,the transistor having a collector connected to an input of the logicgate and the logic gate having an output connected to the base of thetransistor.
 9. An alarm according to claim 5 including means forincreasing the duration of the reference signal when the signallingdevice is on compared to the duration of said reference signal when thesignalling device is off.
 10. Circuitry having signalling means andmeans for actuating the signalling means, said actuating means includinga flip-flop having set and reset inputs and an output, said output beingat one binary logic state when triggered by a pulse at the set input andbeing at the complement state when triggered by a pulse at the resetinput, means for generating input pulses to said reset input, andcircuit means including a monostable multivibrator triggered by a signalat the reset input, said multivibrator producing an output signal ofpredetermined duration, said circuit means applying set pulses to saidset input through the output of said multivibrator, the reset pulsespreventing setting of said flip-flop if received from said generatingmeans at intervals greater than the duration of said multivibratorsignal, said set pulse being of such magnitude and duration as to cancelthe effect of a reSet pulse if an input pulse is received at said resetinput after the duration of said multivibrator signal.